Disposable diapers have met with increased commercial acceptance in recent years primarily because of their convenience, as opposed to cloth diapers, which need to be laundered once soiled. Many different constructions have been proposed and used, and some have met with widespread commercial success in spite of certain inadequacies in functional properties.
One of the most serious prior art problems has been the inability to provide a suitable construction that would keep moisture away from the surface of the diaper which comes into contact with the infant's skin and thereby avoid skin irritation and infection. Mesek et al. U.S. Pat. No. 3,612,055, issued Oct. 12, 1971, discloses several diaper constructions that function extremely well in keeping moisture away from an infant's skin, while at the same time handling a full volume of urine.
These functions are accomplished by a multilayer diaper comprising, in order, a fibrous facing layer which is to be brought into contact with the infant's skin, a layer of highly porous, loosely compacted cellulosic batt, a paper-like, densified, highy compacted cellulosic fibrous layer integral with the loosely compacted batt and an impervious backing sheet adhered to the densified layer throughout the interface therebetween. The facing layer is of porous construction and its fibers have less wettability for water than the fibers of the loosely compacted batt, resulting in a tendency for liquid to flow from the facing web into the batt. The densified fibrous layer has a smaller average pore size than the loosely compacted batt, resulting in a tendency for liquid to flow preferentially from the batt into the underlying densified layer rather than to other areas of the batt, thus tending to restrict wetting in the batt to an area of moderate size. Liquid flowing into the densified layer tends to spread laterally because of its wicking action and liquid which might pass through the densified layer during discharge (when flow is rapid) is held back by the impervious backing sheet for sufficient time to permit absorption to take place. Liquid in excess of the absorptive capacity of the densified layer is forced back by the impervious layer into the dry portion of the loosely compacted batt, thus utilizing the additional absorptive capacity therein.
The facing layer in the above-described diaper is comprised of a mixture of long and short fibers that are held together by a binder having a wetting agent therein which reduces the water repellency of the facing layer, so that urine may readily pass therethrough and into the loosely compacted batt. The binder and wetting agent are uniformly applied across the width and thickness of the facing layer so that the facing layer has uniform functioning properties. While the above type of facing layer has functioned satisfactorily in use, in certain circumstances, particularly when the diaper becomes saturated, there has been a tendency for urine to wick along the facing layer and cause leakage at the edges of the diaper. It has been proposed to obviate this problem by spraying, or otherwise applying, a water-repellent agent on the edges of the facing layer in an effort to prevent urine from wicking outwardly, but this proposal has proven to be unsatisfactory, since the water-repellent agent does not penetrate throughout the thickness of the fabric and hence does not prevent the wicking action.